The use of current mode switching regulators as a means of providing a predetermined and substantially constant output voltage to a varying load from a fluctuating voltage source is well known. An example of such a current mode switching regulator can be found in book by Erickson and Maksimovic, titled “Fundamentals Of Power Electronics,” 2d Edition, Kluwer Academic Publishers, pp. 439-441, (2001).
As is also known, in order to meet stringent efficiency requirements (such as in portable battery operated devices, e.g., cell phones) utilizing a trailing edge current mode switching regulator, component and parameter values are chosen to obtain acceptable ripple at moderate to full load currents. In such a switching regulator, the recirculating device (i.e., low side switch) is typically an active, low voltage drop switch instead of a passive diode in order to improve efficiency. The designs of the known switching regulators usually result in continuous inductor current at all times, which allows for good load voltage regulation and transient response all the way to zero load current and even somewhat negative current (i.e., sinking instead of just sourcing) if required. However, at small load currents, such continuous current operation lowers efficiency due to the relatively large magnitude and duration currents in the switches, inductor and capacitor even when the average load current is near zero. As there is a continuing quest to extend battery life, for example, by the manufacturers of portable devices, there is a need to prevent the efficiency reduction when operating at small load currents. Accordingly, there exists a need to overcome the foregoing problem and to provide a step down current mode switching regulator, which provides for improved efficiency even at small load current conditions, in a cost effective manner.